Response of soil water chemistry to simulated changes in acid deposition in the Great Smoky Mountains

Meijun Cai, Amy M. Johnson, John S. Schwartz, Stephen E. Moore, Matt A. Kulp

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

Watershed recovery from acidic deposition, such as the Noland Divide Watershed in the Great Smoky Mountains National Park, is difficult to predict because of complex biogeochemical processes exhibited in soils. Laboratory soil columns and insitu pan lysimeters were used to investigate soil solution response to simulated reductions in acid deposition. Controlling for influent SO 4 2-, NO 3 -, and NH 4 + concentrations in the column experiments, effluent pH declined similarly to 4.4 among five experimental scenarios from an initial pH of approximately 4.7 and 6.1. Influent-effluent chemical comparisons suggest nitrification and/or SO 4 2- desorption controls effluent pH. Sulfate adsorption occurred when SO 4 2- influent was greater than 25 μmol L -1 and desorption occurred below 15 μmol SO 4 2-, which would equate to approximately a 61% reduction in current SO 4 2- deposition levels. Base cation depletion occurred in column experiments, in which 64-60 μmol L -1 Ca 2+ and 24-27 μmol L -1 Mg 2+ reductions were measured. Cation depletion rates were pH dependent, primarily caused by soil cation exchange and not weathering. In these soils with base saturation below 7%, complete Ca 2+ and Mg 2+ depletion was estimated as 90 to 140years. Protons released by SO 4 2- desorption via ligand exchange are expected to cause further base cation depletion, thereby delaying watershed recovery. Field experiments found SO 4 2- sorption dynamics to be limited by kinetics and hydrologic interflow rates, illustrating how precipitation intensity can influence ion transport from soil to stream. Results from this study provide important information for predicting watershed recovery in the future and suggest needs for further research.

Original languageEnglish (US)
Pages (from-to)617-628
Number of pages12
JournalJournal of Environmental Engineering
Volume137
Issue number7
DOIs
StatePublished - Jul 1 2011

Keywords

  • Acid rain
  • Acids
  • Cations
  • Chemical properties
  • Flow rate
  • Leaching
  • Soil analysis
  • Soil water

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